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Re: journal buffer_credits problem



Hi,

On Wed, 2003-09-24 at 09:13, Akshat Aranya wrote:

> We need to be careful to not perform file system operations that are 
> specific to the semantics of one particular file
> system. Is there any way that you suggest that can get us a nested 
> transaction (through a VFS operation or an operation exposed by the file 
> system to VFS) when there's a transaction already associated with the 
> current process?

No.

Trouble is, transactions need to be atomic (of course!) but there's only
finite space in the journal.  We need to know, *before* the transaction
starts, whether or not there is space for the transaction in the current
journal segment, or whether we have to start a new compound transaction
in the journal and potentially do a checkpoint to evict some old space.

That's why we can't grow an existing open transaction (or rather, we
can't _guarantee_ it --- there are functions to try to expand a
transaction so that long-running operations like truncating huge files
can try to stay within a single transaction, but the expand can always
fail.)

Cheers,
 Stephen




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